`accuracy` metric is no longer supported

[AmitMY]

Training translation model with VQ outputs, perplexity is not a great fit for dev set evaluation, and bleu or others is also not great.
What I really want to use is accuracy - that gets the accuracy for all predicted factors - but even if just the main token, that would be great.

in constants, a metric named accuracy is declared and set up, but it is never reported anywhere.

AssertionError: Early stopping metric accuracy not found in validation metrics.

I would love to see accuracy supported again, and not removed.